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https://github.com/haimgel/display-switch

Turn a $30 USB switch into a full-featured multi-monitor KVM switch
https://github.com/haimgel/display-switch

ddc macos monitor-configuration rust-lang switches-monitors windows

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Turn a $30 USB switch into a full-featured multi-monitor KVM switch

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# Turn a $30 USB switch into a full-featured KVM



This utility watches for USB device connect/disconnect events and switches monitor inputs via DDC/CI. This turns

a simple USB switch into a full-fledged KVM solution: press one button on your USB switch and all your monitors

connect to a different input.



It is supposed to be installed on all computers that could be connected to these monitors, since the app only switches

monitors "one way" and relies on itself running on the other computers to switch it "the other way" as needed.

 

## Platforms supported



The app should function on MacOS (Intel Macs only), Windows, and Linux.



**NOTE:** Display Switch is currently **not** working on M1 Macs: M1 series SoC support in `ddc-macos-rs` is planned but is not 

[implemented yet](https://github.com/haimgel/ddc-macos-rs/issues/2).



## Configuration



The configuration is pretty similar on all platforms:



On MacOS: the configuration file is expected in `~/Library/Preferences/display-switch.ini`

On Windows: the configuration file is expected in `%APPDATA%\display-switch\display-switch.ini`

On Linux: the configuration file is expected in `$XDG_CONFIG_HOME/display-switch/display-switch.ini` or `~/.config/display-switch/display-switch.ini`



Configuration file settings:



```ini

  usb_device = "1050:0407"

  on_usb_connect = "Hdmi1"

  on_usb_disconnect = "Hdmi2"

```



`usb_device` is which USB device to watch (vendor id / device id in hex), and `on_usb_connect` is which monitor input

to switch to, when this device is connected. Supported values are `Hdmi1`, `Hdmi2`, `DisplayPort1`, `DisplayPort2`, `Dvi1`, `Dvi2`, `Vga1`.

If your monitor has an USB-C port, it's usually reported as `DisplayPort2`. Input can also be specified as a "raw"

decimal or hexadecimal value: `on_usb_connect = 0x10`



The optional `on_usb_disconnect` settings allows to switch in the other direction when the USB device is disconnected.

Note that the preferred way is to have this app installed on both computers. Switching "away" is problematic: if the

other computer has put the monitors to sleep, they will switch immediately back to the original input.



### Different inputs on different monitors

`display-switch` supports per-monitor configuration: add one or more monitor-specific configuration sections to set

monitor-specific inputs. For example:



```ini

on_usb_connect = "DisplayPort2"

on_usb_disconnect = "Hdmi1"



[monitor1]

monitor_id = "len"

on_usb_connect = "DisplayPort1"



[monitor2]

monitor_id = "dell"

on_usb_connect = "hdmi2"

```



`monitor_id` specifies a case-insensitive substring to match against the monitor ID. For example, 'len' would match

`LEN P27u-10 S/N 1144206897` monitor ID. If more than one section has a match, a first one will be used.

`on_usb_connect` and `on_usb_disconnect`, if defined, take precedence over global defaults.



_Tips for Windows_: monitors can be renamed in the Registry at

`\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\DISPLAY\{MODEL_ID}\{CONNECTION_ID}`. Edit the `DeviceDesc` value and change the name after the last semicolon. This is especially helpful in case they are all just "Generic PnP Monitor".



### Running external commands

`display-switch` supports running external commands upon connection or disconnection of USB devices. This configuration

can be global (runs every time a configured USB device is connected or disconnected) or per-monitor (runs only when

a given monitor is being switched):



```ini

usb_device = "1050:0407"

on_usb_connect = "Hdmi1"

on_usb_disconnect = "DisplayPort2"

on_usb_connect_execute = "echo connected"

on_usb_disconnect_execute = "echo disconnected"



[monitor1]

monitor_id="foobar"

on_usb_connect_execute = "echo usb connected, monitor 'foobar' being switched"

on_usb_disconnect_execute = "'c:\\program files\\my app.exe' --parameter"

```



Notes: 

1. External applications are executed as the same user that started `display-switch`. 

2. This program supports splitting supplied configuration into application name and parameters, but no other shell features are supported.

3. If the application path contains spaces, surround the full file path with single quotes.

4. On Windows, escape the backslashes (replace \ with \\, see the example above).



### USB Device IDs



#### Windows

To locate the ID of your USB device ID on Windows:

1. Open Device Manager

2. Locate the USB device, view the properties

3. Switch to the *Details* tab and select *Hardware IDs* in the Property dropdown

4. You should see a value similar to `HID\VID_046D&PID_C52B&MI_00` (the exact values will differ) - the USB device ID is a combination of the *Vendor ID* and the *Product ID* - for example, in this case it would be `046D:C52B`



#### MacOS

To locate the ID of your USB device ID on MacOS, open a terminal and run the following:

```bash

brew install lsusb



$ lsusb > a



$ lsusb > b

$ opendiff a b

```

In the command output, the highlighted lines show you which USB IDs are most relevant.



#### Linux

Requires additional packages, install via: `sudo apt install libxi-dev xorg-dev`



To locate the ID of your USB device on Linux, first install `lsusb`, which your Linux

distro should have a package for. (On Debian, Ubuntu and RedHat, the package name is `usbutils`.)

Then, in a terminal, run the following:

```

$ lsusb > a



$ lsusb > b

$ diff -u a b

```

The diff output will show which USB IDs are most relevant.



## Logging



* On MacOS: the log file is written to `/Users/USERNAME/Library/Logs/display-switch/display-switch.log`

* On Windows: the log file is written to `%LOCALAPPDATA%\display-switch\display-switch.log`

* On Linux: The log file is written to `$XDG_DATA_HOME/display-switch/display-switch.log`

 or `~/.local/share/display-switch/display-switch.log`



## Building from source



### Windows



[Install Rust](https://www.rust-lang.org/tools/install), then do `cargo build --release`



### MacOS



[Install Xcode](https://developer.apple.com/xcode/), [install Rust](https://www.rust-lang.org/tools/install), then do

`cargo build --release` 



### Linux



[Install Rust](https://www.rust-lang.org/tools/install), then do `cargo build --release`



## Running on startup



### Windows



Copy `display_switch.exe` from `target\release` (where it was built in the previous step) to 

`%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup`.



### MacOS



```bash

  # Get your INI file in order! (see above)

  cp target/release/display_switch /usr/local/bin/

  cp dev.haim.display-switch.daemon.plist ~/Library/LaunchAgents/

  launchctl load ~/Library/LaunchAgents/dev.haim.display-switch.daemon.plist

```

### Linux

Copy built executable:



```bash

  cp target/release/display_switch /usr/local/bin/

```

Enable read/write access to i2c devices for users in `i2c` group. Run as root :



```bash

groupadd i2c

echo 'KERNEL=="i2c-[0-9]*", GROUP="i2c"' >> /etc/udev/rules.d/10-local_i2c_group.rules

udevadm control --reload-rules && udevadm trigger

```



Then add your user to the i2c group :



```

sudo usermod -aG i2c $(whoami)

```



Create a systemd unit file in your user directory (`/home/$USER/.config/systemd/user/display-switch.service`) with contents



```

[Unit]

Description=Display switch via USB switch



[Service]

ExecStart=/usr/local/bin/display_switch

Type=simple

StandardOutput=journal

Restart=always



[Install]

WantedBy=default.target

```



Create the config file at `/home/$USER/.config/display-switch/display-switch.ini`.

Then enable the service with



```bash

systemctl --user daemon-reload

systemctl --user enable display-switch.service

systemctl --user start display-switch.service

```